1. Field of the Invention
The invention relates to a so-called dielectric barrier discharge-lamp, which is used, for example, as an ultraviolet light source for a photochemical reaction, and in which light radiated from "excimer" molecules, which are formed by a dielectric barrier discharge, is used.
2. Background of the Disclosure
As generic art, a radiator, i.e., a dielectric barrier discharge lamp, is known, for example, from JP laid-open specification HEI 2-7353 or U.S. Pat. No. 4,837,484, in which a discharge vessel is filled with a discharge gas forming "excimer" molecules and in which "excimer" molecules are formed by a dielectric barrier discharge, which is also designated as ozone production discharge or as silent discharge, as is described in "Discharge Handbook," Electrogesellschaft (Electric Company), June 1989, 7th Edition, page 263. In the radiator, light is radiated from the "excimer" molecules.
In the above-named publications, an arrangement of a dielectric barrier discharge lamp is described, in which the discharge vessel has a cylindrical shape and functions at least partially also as dielectric of the above-described dielectric barrier discharge, which is at least partially transparent relative to the light radiated from the above-described "excimer" molecules. In this discharge lamp, further, the above-described light-transmitting dielectric is provided at least partially with netlike electrodes.
Further, another design of a dielectric barrier discharge lamp is known, which has an approximately cylindrical outer shape as well as an overall hollow cylindrical discharge vessel, in which an external tube and an internal tube are arranged coaxially to one another, a discharge space exists between the external tube and the internal tube and a hollow space is formed inside the internal tube.
The above-described dielectric barrier discharge lamps have various advantages, which neither conventional low-pressure mercury discharge lamps nor conventional high-pressure arc discharge lamps have, such as, for example, a radiation of ultraviolet rays with short waves, in which main wavelengths lie at 172 nm, 222 nm and 308 nm, and at the same time a selective production of light with individual wavelengths with a high efficiency, which are, for example, line-spectrum-like.
However, a conventional dielectric barrier discharge lamp had the drawback that a space uniformity of light output, a time stability and a light yield were not always obtained to a sufficient degree.
Further, it was regarded in this connection as disadvantageous that despite the lamp arrangement that is completely different from the conventional low-pressure mercury discharge lamp or the conventional high-pressure arc discharge lamp, no adequate examination of a coefficient of utilization of the light or of a maintenance of the lamp was performed.
Such a dielectric barrier discharge lamp is used for reforming plastic surfaces, for forming layers or for similar purposes, and it is often used within an atmosphere in addition to air, such as, for example, within an atmosphere of nitrogen, argon, oxygen or the like. In this connection, however, it was regarded as disadvantageous that:even though a dielectric barrier discharge lamp of hollow cylinder type allowed to linger in the air is introduced in a nitrogen atmosphere, air present inside the internal tube forming the hollow cylinder is emitted by steps in the nitrogen within a short time, without being substituted with the nitrogen, and without the nitrogen atmosphere being contaminated by the air.
In this case, a suitability because of a high reliability is achieved, if the netlike electrodes arranged in the external tube are put on an earth potential and a high voltage is applied to the electrodes arranged in the internal tube. But in this case, it is regarded as disadvantageous that dust accumulates on the electrodes and that the accumulated dust precipitates as a mass on an object to be treated and contaminates it, since the electrodes, to which the high voltage is applied, have a dust-catching effect.
The above-described drawbacks are characteristic for a dielectric barrier discharge lamp, which has a hollow cylindrical discharge space, which is designed so that an external tube as well as an internal tube with approximately cylindrical outer shapes are arranged coaxially to one another. These drawbacks occur especially when using the dielectric barrier discharge lamp for the purpose of a photochemical reaction.